Descriptions

BACKGROUND: The giant lizard of La Gomera (Gallotia bravoana), is an endemic lacertid of this Canary Island that
lives confined to a very restricted area of occupancy in a steep cliff, and is catalogued as Critically Endangered by
IUCN. We present the first population genetic analysis of the wild population as well as of captive-born individuals (for
which paternity data are available) from a recovery center. Current genetic variability, and inferred past demographic
changes were determined in order to discern the relative contribution of natural versus human-mediated effects on
the observed decline in population size.
RESULTS: Genetic analyses indicate that the only known natural population of the species shows low genetic diversity
and acts as a single evolutionary unit. Demographic analyses inferred a prolonged decline of the species for at least 230
generations. Depending on the assumed generation time, the onset of the decline was dated between 1200–13000
years ago. Pedigree analyses of captive individuals suggest that reproductive behavior of the giant lizard of La Gomera
may include polyandry, multiple paternity and female long-term sperm retention.
CONCLUSIONS: The current low genetic diversity of G. bravoana is the result of a long-term gradual decline. Because
generation time is unknown in this lizard and estimates had large credibility intervals, it is not possible to determine the
relative contribution of humans in the collapse of the population. Shorter generation times would favor a stronger
influence of human pressure whereas longer generation times would favor a climate-induced origin of the decline. In
any case, our analyses show that the wild population has survived for a long period of time with low levels of genetic
diversity and a small effective population size. Reproductive behavior may have acted as an important inbreeding
avoidance mechanism allowing the species to elude extinction. Overall, our results suggest that the species retains its
adaptive potential and could restore its ancient genetic diversity under favorable conditions. Therefore, management of
the giant lizard of La Gomera should concentrate efforts on enhancing population growth rates through captive
breeding of the species as well as on restoring the carrying capacity of its natural habitat.